(a) Field of the Invention
The embodiments of the present invention relate to a plasma display device and a driving method thereof. Specifically, embodiments of the present invention relate to a plasma display device for reducing flicker and a driving method thereof.
(b) Description of the Related Art
Flat panel displays such as liquid crystal display devices (LCDs), field emission displays (FEDs) and plasma display devices are actively being developed. Plasma display devices in flat panel displays have better brightness, luminescent efficiency and wider viewing angles in comparison to other types of flat panel displays. Therefore, plasma displays have been focused on as substitutes for the conventional cathode ray tubes (CRTs) in large display devices such as display devices that are greater than 40 inches in size.
A direct current (DC) plasma display device has electrodes that are exposed to a discharge space without insulation, thereby causing a current to directly flow through the discharge space during the application of a voltage to the electrodes. Therefore, a problem with such a DC plasma display device (PDP) is that it requires a resistance for limiting the current. On the other hand, an alternating current (AC) plasma display device has electrodes that are covered with a dielectric layer, which forms a natural capacitance component that restricts the current and protects the electrodes from the impact of ions during discharge. As a result, the AC plasma display device has an advantage over the DC plasma display device because it has a longer lifetime.
As shown in FIG. 1, the above-noted plasma display device divides one frame of an input video signal data into a plurality of subfields and combines the subfields to express grayscale levels. Each subfield has a reset period, an address period and a sustain period. The reset period is for initializing the status of each discharge cell so as to facilitate an addressing operation on the discharge cell. The address period is for applying an address voltage to cells to be turned-on (i.e., addressed cells) to accumulate wall charges in these cells. Cells that do not have the address voltage applied to them are not selected to be turned-on cells. The sustain period is for applying a sustain discharge pulse or set of pulses to perform a discharge for displaying images via the turned-on cells selected during the address period.
FIG. 1 illustrates one frame that is divided into eight subfields to express 256 different grayscale levels. Each subfield (SF1-SF8) includes reset periods (not shown), address periods (A1-A8) and sustain periods (S1-S8). The sustain periods (S1-S8) have emission periods with durations of 1T, 2T, 4T, . . . , 128T where T is a unit of time. The emission periods have different individual durations with the combined ratio of 1:2:4:8:16:32:64:128.
For example, a grayscale level of 3 is expressed by discharging a discharge cell during a first subfield (SF1) having an emission period with a duration of 1T and a second subfield (SF2) having an emission period with a duration of 2T so as to have a total emission period with a duration of 3T. In this way, a combination of different subfields, each having different emission periods, produces pictures having 256 different grayscale levels.
Expression of grayscale levels by the plasma display device generates flicker that is detectable by human vision. The flicker is more easily detected when the screen size becomes larger or its refresh frequency is low. A plasma display device generates a large amount of flicker when generating phase alternation line (PAL) images when the two above-noted conditions are present. In this case, the flicker can only be reduced by controlling (i.e. increasing) the frequency, because the screen size cannot be modified.
As shown in FIG. 2, subfields of one frame are divided into two groups, G1 and G2, each with the same arrangement of subfield weights except that the least significant bit (LSB) subfield in each group differs. This scheme reduces flicker that is generated by a large screen plasma display device that uses 50 Hz video signals. This scheme is more efficient in reducing flicker than the conventional arrangements of subfields such as the minimum increment arrangement or the minimum decrement arrangement. However, the scheme shown in FIG. 2 may generate flicker at specific grayscale levels because it cannot divide the amount of emitted light into two equal smaller amounts.